U.S. Pat. No. 6,571,756 discloses a membrane-controlled two-stroke engine which draws an air/fuel mixture into the crankcase via an inlet and inducts fuel-free fluid such as pure air into the transfer channel via a membrane-controlled fluid channel. Pure air passes from the transfer channel window into the crankcase at the crankcase end of the transfer channel whereby the mixture, which is stored in the crankcase, is made lean. A corresponding quantity of oil must be supplied to the crankcase with the fuel in order to ensure an adequate lubrication of the moving parts in the crankcase. This leads to a coking in the muffler as well as in the combustion chamber and causes poor exhaust-gas values.
European patent publication 0,302,045 discloses an internal combustion engine having crankcase scavenging wherein the necessary combustion air is drawn by suction via the crankcase and the fuel, which is needed for operation, is injected into the combustion chamber via an injection nozzle in the region of the inlet window. An operation of a two-stroke engine of this kind requires, however, a separate lubrication system in the crankcase which is complex and can lead to an increased entry of oil into the combustion chamber.